I used to import data from a http site but recent days, the site switch to https and I got an error code when importing data from that site.

How to fix it?

Error is like that:
Code:
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification pa
> th to requested target
could not open url
My code to import data from that site
Code:
import delimited https://thatsite/file.txt, delimiter(tab, collapse) clear
I found this package but still can not use it to import data: https://www.ssc.wisc.edu/sscc/pubs/readhtml.htm

Thank you all.